IssueTracker

Cloud Build GitLab pull request triggers are being triggered by events that are expected not to:

- Comments
- Editing labels
- Editing reviewers
- Editing assignees
- Editing a PR title
- Editing a PR description
- Approving a PR (note, dismissing a review and requesting changes doesn't trigger)

Also, some of the substitutions are not populating as expected:

- BRANCH_NAME is set to an empty value in the PR trigger. It is not shown in the build details.
- REPO_FULL_NAME only includes the “<sub-group>/<repo-name>”. It should include the user or organization.